1. Field of the Invention
The present invention relates to a holding mechanism for holding a wafer that is a target object to be processed.
2. Related Art
Conventionally, a wafer divided along predicted separation lines into individual devices such as ICs, LSIs and the like is cut by a cutting blade along the separation lines so that the wafer separates into individual devices. However, it is difficult for the cutting blade to dice the wafer into separate devices when, for example, the wafer is formed of a material high on the Moh's hardness scale, such as a sapphire substrate.
Accordingly, recently, a technique involving directing a pulse laser onto the separation lines, forming grooves in such separation lines and separating the wafer into the individual devices has been proposed (for example, JP-A-10-305420).
However, even with the use of a laser of a wavelength that has a high rate of absorption by the wafer, most of the light permeates the wafer and reaches a chuck table that suctionally holds the wafer in place, damaging the chuck table.
Moreover, when protective tape is affixed to the surface of the wafer, heating of the chuck table by the laser beam, heats the protective tape and causes it to melt, which not only makes it difficult to transport the wafer from the chuck table but also causes the melted protective tape to adhere to the chuck table, thereby dirtying the chuck table and adversely affecting future use.
At the same time, attempting to make the chuck table out of a material with a high rate of absorption of the laser beam makes it difficult to open fine holes in the material that are used to transmit a suction force to the wafer.